The present invention relates generally to devices, systems and methods for providing illumination control. More particularly, the present invention relates to systems capable of detecting occupancy and accordingly regulating an illumination level in a defined area.
Lighting control systems are known in the art which receive and implement occupancy information in order to regulate lighting output accordingly. The use of occupancy sensors in lighting control has been on a steady rise as the industry advances towards more aggressive energy conservation measures. Conventional occupancy sensors are known which utilize various detection methods for detecting occupancy in a defined area. Among the known methods, passive infrared (PIR), microwave Doppler shift, ultrasonic Doppler shift, and audio sensors are the most common.
Passive infrared (PIR) sensors are considered to be the most common type of occupancy sensor. They are able to “see” heat emitted by occupants, and triggering occurs when a change in infrared levels is detected, such as when a warm object moves into or out of view with respect to the sensor's eyes. PIR sensors are very resistant to false triggering. Although some PIR sensors have an operating range of up to 35 feet in specific directions under ideal conditions, they are most reliable within a 15-foot range. This is due to the blind spots between their wedge-shaped sensory patterns becoming wider with increasing distance. The sensor is most sensitive to movements laterally across the field of view. They are passive, meaning that they do not send out any signal, and depend on the intensity of the heat from the moving part of the subject, which attenuates by the square of the distance.
PIR occupancy sensors typically use PIR elements with two to six areas. Fresnel lenses focus a projection of the defined area on the PIR element. Output of each area on the PIR element is amplified electronically. Differential amplification is used so that a higher common-mode rejection ratio (CMRR) may be achieved. The CMRR is a measure the tendency of a device to reject input signals common to both input leads, and is defined as the ratio of the powers of the differential gain over the common-mode gain, as measured in positive decibels. In other words, differences between values of different areas of the PIR element are amplified and the common factor, which is present due to IR emissions from other surfaces and objects, is rejected in the amplifier. Thus, once a heat-emitting source crosses the sensitive areas, the projection is drifted from one PIR area to another. This will result in a pulse at the output of the amplifier. The pulse is then compared to a desired threshold to filter the effect of thermal and electronic noises. Various coverage patterns can be achieved via modifications to the construction of the Fresnel lens.
There has been an extensive amount of research and development conducted to implement and improve performance and accuracy of occupancy detection. Accordingly, various sensing technologies employ two or more detection methods in a single system to reduce false tripping. Dual technology occupancy sensors generally use an active sensing method in combination with a PIR element. Microwave and ultrasound are widely used active sensing technologies. Both methods rely on processing Doppler shifts between the frequency of transmitted and reflected signals.
To achieve a completely passive dual technology sensor, a design as previously known in the art employs a PIR sensor as a primary detector and a microphone as a secondary detector. This enhances the accuracy of the sensor through detecting spontaneous changes in the amplitude of the noise in the defined area. The signal from the microphone used in this sensor is amplified by an automatic gain control amplifier, and accordingly consistent background noises are filtered out. The microphone module is activated by the PIR module, or in other words the lights will be turned on when the PIR element senses a motion. Once in the ON state, either one of the PIR or microphone modules will keep the lights in the ON state. Once motion has not been sensed for a predetermined period of time (timeout), the lights will be put into the OFF state and a grace period timer may be activated. During this grace period, the lights could be reverted into the ON state by a signal from the microphone as well as from the PIR module. Once in the OFF state, the microphone will not regulate the lights into the ON state. It is the PIR module that re-initiates the ON state and also activates the microphone.
However, occupancy sensors and associated systems or networks as are conventionally known in the art still typically share a common failure regarding false triggering. This is particularly true where multiple light fixtures and associated lighting devices are networked together across a plurality of independently defined areas within a collective area such as a parking garage. For example, sensors in a first area may likely fail to detect occupants in a second area and trigger the lights off while the collective area is still occupied.
In one conventional example, a wireless system 10 (point-to-point or mesh) may be employed as represented in FIG. 1. A primary controller 11 as shown includes a transceiver 14 operatively linked via a bi-directional wireless communications network 16 to respective transceivers 15a-15f for each of a plurality of lighting devices 13a-13f. The devices 13a-13f each receive mains power from mains wires 12a, 12b, and also include a respective one of a plurality of occupancy sensors 17a-17f. However, there are numerous disadvantages to such a configuration. Guaranteeing coverage for wireless RF is sometimes difficult due to construction and distances between devices, wherein potential attenuation and multipath problems may typically arise. Mesh networks also generally require commissioning and are often difficult to troubleshoot.
In another conventional example, a system 20 as represented in FIG. 2 may be provided with dedicated control wires 24a, 24b extending from a primary controller 21 to each of the plurality of lighting devices 23a-23f. However, this configuration also includes numerous disadvantages, including but not limited to the cost of material and labor to run dedicated control wires. It also may not be possible to run control wires in retrofit applications.
In still another conventional example, a system 30 as represented in FIG. 3 is provided with control signals imposed via bi-directional power line communications (via mains wires 32a, 32b). However, disadvantages to this configuration include but are not limited to the cost of the bidirectional communication modems 34 needed in the controller 31 and at each luminaire 33. The integrated circuits which would typically support such an approach are relatively expensive and would likely require additional time/effort/expertise to commission.